Properties of unidirectional GFRPs based on an epoxy resin modified with polysulphone or an epoxyurethane oligomer

The mechanical properties of unidirectional GFRPs based on an ED-22 epoxy resin were investigated. The resin was modified with a PSK-1 polysulphone or a PEF-3a epoxyurethane oligomer. Triethanolaminotitanate or diaminodiphenilsulphone was used as a hardener. The modification did not improve the mechanical properties of GFRPs in quasi-static loading; but in a low-speed impact loading, the shear strength of epoxypolysulphone GFRPs with 20 wt.% PSK-1 increased by 20–25%. For all the GFRPs investigated, the shear strength grew linearly with the logarithm of loading rate. The introduction of the modifiers increased the fracture toughness considerably: by 100 and 70% for GFRPs modified with 20 wt.% PSK-1 and 50 wt.% PEF-3a, respectively. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp.739–758, November–December, 2006.     

The Effect of an Active Diluent on the Properties of Epoxy Resin and Unidirectional Carbon-Fiber-Reinforced Plastics

The influence of an active diluent on the properties of an epoxy matrix and carbon-fiber-reinforced plastics (CFRP) is investigated. The physicomechanical properties of an ED-20 epoxy resin modified with diglycidyl ether of diethylene glycol (DEG-1), the adhesion strength at the epoxy matrix–steel wire interface, and the mechanical properties of unidirectional CFRP are determined. The concentration of DEG-1 was varied from 0 to 50 wt.%. The properties of the matrix, the interface, and the composites are compared. It is stated that the matrix strength affects the strength of unidirectional CFRP in bending and not their strength in tension, compression, and shear. The latter fact seems somewhat unexpected. The interlaminar fracture toughness of the composites investigated correlates with the ultimate elongation of the binder. A comparison between the concentration dependences of adhesion strength and the strength of CFRP shows that the matrices utilized provide such a high interfacial strength that the strength of CFRP no longer depends on the adhesion of its constituents.     

New Potentialities in Producing Composites Reinforced with High-Strength High-Modulus Polyethylene Fibers

A concept of physical and chemical stages of interaction between the matrix and reinforcing fibers during the production of composite materials is introduced. A strong bond between these constituents is formed at the stage of chemical interaction, which is characterized by a certain value of activation energy. The activation energy of such an interaction for high-strength high-modulus polyethylene fibers used for reinforcing composites is estimated. Based on these estimates, conditions for fiber activation with cold plasma are found. The application of plasma-activated polyethylene fibers for reinforcing an epoxy matrix allows one to produce light-weight composites with high physicomechanical indices. The failure mode of such composites points to a high strength of the bond between the fibers and matrix. The data on treating the fiber surface with cold plasma above the activation energy of chemical interaction may be utilized to create new types of organic composites from other kinds of organic fibers and matrices.     

Determination of the Interlaminar Fracture Toughness of Glass-Fiber-Reinforced Plastics on Ring Segments

A method is developed which allows one to estimate the fracture toughness G _{I c} of fiber-reinforced plastics using ring segment specimens. It is shown that this method reduces to the so-called angle method. The approach developed was tested on segments of glass-fiber-reinforced plastic (GFRP) rings based on an EDT-10 epoxy matrix and RVMPN 10-1200-14 glass fibers. The crack was set by a polyimide film placed in the specimen midlayer at the winding stage. The ring thickness was 1 to 4.5 mm. The fracture toughness G _{I c} was also calculated from force F-displacement D diagrams. It was found that the values of G _{I c} determined by both methods agreed well. For 2 mm thick segments with long (L 30 mm) cracks, G _{I c} was practically independent of L and , and, for the GFRP examined, it could be regarded as a material constant.     

Properties of Filament-Wound Organoplastics Based on Epoxy Polysulfone Matrices and Armos and Rusar Aramid Fibers

The properties of unidirectional filament-wound organoplastics based on ED-22 epoxy oligomer modified by PSK-1 polysulfone and Rusar or Armos aramid filaments were studied. It was shown that the modification of ED-22 epoxy resin with PSK-1 thermoplastic increases significantly (2.5 times) the fracture toughness of the studied organoplastics. The introduction of PSK-1 in ED-22 increases the shear strength of organoplastics from 20 to 60% depending on the type of fibers and the loading speed. For organoplastics based on filaments of different linear density, the efficiency of the introduction of PSK-1 polysulfone depends on the degree of penetration of binder into the interfiber space.